1. Field of the Invention
The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell capable of performing power generation of high efficiency, using hydrocarbon or a steam reformed gas containing hydrogen and carbon monoxide as main components, obtained by complete reforming of hydrocarbon as fuel.
2. Prior Art
Generally, a solid oxide fuel cell is an assembly consisting of a plurality of unit cell structures each comprising a solid electrolyte provided between electrode plates, i.e. a positive pole, which will be hereinafter referred to as an air electrode, and a negative pole, which will be hereinafter referred to as a fuel electrode, where a hydrogen gas, which will be hereinafter referred to merely as hydrogen, is supplied to the fuel electrode of the fuel cell as fuel and air (oxygen) is supplied to the air electrode as an oxidizing agent and the hydrogen reacts with the oxygen through the electrolyte, thereby generating an electromotive force (electric energy).
The solid oxide fuel cell has a high power generation with low pollution and highly expected practical applications in various domestic and industrial fields. Heretofore, researches and developments have been made on constituent materials of solid oxide fuel cells directed to hydrogen as fuel, and thus sintered nickel zirconia cermet has been widely used, for example, for the fuel electrode.
For practical application of solid oxide fuel cells, however, it is necessary to conduct power generation of high efficiency with fuel obtained by steam reforming of hydrocarbon as a raw material. Thus, it is necessary to conduct efficient power generation even with carbon monoxide in the reformed gas together with hydrogen. Still furthermore, it is preferable to directly conduct steam reforming on the fuel electrode on the basis of the cell working temperature, thereby making the reformer as small as possible and carrying out power generation of high efficiency even with partially steam-reformed raw material, or to conduct steam reforming only by the fuel electrode without using any reformer at all, thereby carrying out power generation of high efficiency. Thus, it is required that the fuel electrode has a good electrode activity to not only hydrogen, but also carbon monoxide and a good steam reforming activity to hydrocarbon. However, the conventional sintered porous nickel zirconia cermet has no satisfactory electrode activity to carbon monoxide and consequently has a low steam reforming activity to hydrocarbon as problems.